Mammalian body implants, such as corneal prostheses, (also known as keratoprostheses), are very useful to replace degenerated or injured mammalian tissue if the remainder of the mammalian body accepts the presence of such implant and if the biocompatible implant performs the function of the replaced tissue in an acceptable manner.
Corneal prostheses are especially vital for the continued functioning of a mammal, especially a human being, because a degenerated or injured cornea obscures vision.
While there have been attempts to provide synthetic corneal prostheses, currently none are deemed acceptable by governmental regulatory agencies due to their inability to provide an acceptable replacement for natural cornea transplants obtained from cadavers. Often these devices have failed because of erosion and necrosis of the adjacent tissue, chronic inflammation and epithelialization of the anterior chamber.
Optimally, the anterior surface of a keratoprosthesis should support the adherence and proliferation of corneal epithelial cells, resulting in an intact epithelial layer which is continuous with the surrounding host epithelium. A continuous layer of epithelium permits maintenance of the normal precorneal tear film, ensures a good optical surface and provides a barrier against microbial invasion.
A prior effort has been to provide a corneal prosthesis using poly(vinyl alcohol) hydrogel as an optical element and a porous outer skirt secured to the periphery of the element. European Patent Publication 0 333 344 (Capecchi et al.), the European counterpart to U.S. Pat. No. 5,108,428 discloses this corneal prosthesis and identifies the desire to coat or laminate the anterior surface with a basement membrane component(s) to facilitate growth of epithelial cells on it. Coating is preferably performed by adsorption or chemical attachment or integration during polymerization with basement membrane component(s) prior to seeding of corneal epithelial cells on the anterior surface. Acceptable basement membrane components include laminin, fibronectin, Type I collagen, Type IV collagen, or a cell-free extract prepared from extracellular matrix of corneal epithelial cells.